Crystallization behavior and solid-state microstructure of poly(hexamethylene succinate) (PHS) and its phosphorus-containing copolyesters with bulky pendent group (DDP) have been investigated. The molecular weight, chemical structure and composition of the copolyesters were characterized and confirmed by GPC, H-1 and P-31 NMR. WAXD results suggest that the bulky DDP comonomer units in the copolyesters are noncrystallizable and are extruded from the crystal lattice of PHS. POM observations indicate that the spherulitic morphology becomes irregular and blurry with an increase of the DDP content. The kinetics analysis of isothermal crystallization shows that the crystallization of the copolyesters is retarded by the presence of the bulky DDP comonomer units. The observed crystallization and melting temperatures of the copolyesters are progressively depressed with the increase of DDP. SAXS quantitative analysis provides a proof that the significant increase in the long period of the copolyesters mainly arises from the increase in the amorphous layer, because the thickness of the lamellar increases slightly. A model of the lamellar crystal structure of the copolyester is proposed for its depression of the equilibrium melting temperature. (C) 2015 Elsevier Ltd. All rights reserved.